We kind of warm up to summer, and then it's moderately hot for a while. Then the summer rains come and cool things down. Then, it's the normal ridiculously hot summer weather that makes you sweat your whole shirt out just walking down the street. But the good part is that this crazy hot time, doesn't actually last very long. It's only about a month. Then, Korea returns to just moderately hot, and then, before you know it we're back to the beautiful just-right weather of fall.
(Because of this gentle slope upward to the uncomfortable summer highs, many Koreans simply opt out of home air conditioning. They figure that they can just tough it out for a month or so.)
Summer is hot, but not too hot - at least most of the time. I love this about Korea.